Rotor of brushless direct-current motor

ABSTRACT

A permanent magnet rotor of a brushless direct current (BLDC) motor, in which cogging torque ripple and electromagnetic vibration noise transferred to the permanent magnet rotor can be blocked and a motor&#39;s power-to-weight ratio can be improved. A conventional BLDC motor has to use an electric steel sheet core so as to maintain the maximum magnetic flux density of the permanent magnet rotor and to minimize a rotating electric field loss. As a result, cogging torque vibration is unavoidably transferred to a load side through the motor rotary shaft. However, the rotor can enable stable driving of the BLDC motor by innovatively blocking the cogging torque vibration and the electromagnetic vibration noise and can greatly reduce the motor&#39;s weight by using a plastic or non-magnetic material instead of an electric steel sheet core.

BACKGROUND

1. Field

One or more aspects of the embodiments discussed herein relates to arotor of a brushless direct-current (hereinafter, referred to as “BLDC”)motor, and more particularly, to a rotor of an BLDC motor, which canprevent electromagnetic vibration and noise generated between a rotorand an armature from being transferred to a rotary shaft of the rotorduring the motor driving to thereby minimize motor noise and can reducethe weight of the rotor to thereby maximize a motor's power-to-weightratio.

2. Description of the Related Art

Generally, a conventional rotor of a brushless direct-current (BLDC)motor uses a permanent magnet and a rotor core is necessarily combinedwith a rotor shaft using a ferromagnetic body or an electric steel sheetin order to form a magnetic circuit of the permanent magnet.

However, when the permanent-magnet rotor generates a rotation torque dueto its interaction with a rotating magnetic field of an armature,electromagnetic cogging generated in an air gap between the rotor andthe armature, torque ripple, or vibration caused by the interaction ofelectromagnetism is directly transferred to the rotor shaft and may bethen transferred to the load side or may be amplified, thereby causingsevere mechanical noise such as resonance noise.

An explanation of the rotor structured as described above will be indetail given. FIGS. 1A and 1B illustrate the structure of a rotor of aconventional BLDC motor, and FIG. 2 illustrates a magnetic circuit of arotor and an armature 5 of a conventional BLDC motor.

As illustrated in FIGS. 1A and 1B, the rotor of the conventional BLDCmotor has a structure in which a radially magnetized C-type permanentmagnet 10 is attached to the outer circumferential face of an electricsteel sheet ferromagnetic core portion 12 made of a ferromagnetic ironcore or armature and a rotor shaft 14 is inserted into a central portionof the ferromagnetic core portion 12.

The C-type permanent magnet 10 is an anisotropic magnet that ismagnetized radially around the center of the rotor shaft 14. In order toform a magnetic circuit 102 with a different pole of the rotor, theC-type permanent magnet 10 has to have a ferromagnetic material such aspure iron or an electric steel sheet core provided on its innercircumferential face in FIG. 2.

When the rotor in which the ferromagnetic core portion 12 and the C-typepermanent magnet 10 are combined with each other is assembled onto thecenter of the armature 5, the magnetic circuit 102 through which fluxflows is formed as illustrated in FIG. 2. When the pole shift of thearmature 5 occurs in magnetic coupling of the formed magnetic circuit102, the rotor rotates due to interaction torque of a rotating magneticfield.

At this time, vibration caused by unbalance among magnetic fluxdensities of an air gap 105, a slot portion 15 of the armature 5, and agap portion 16 of the permanent magnetic 10 of the rotor and magnetizingvibration caused by pole shift of the armature 5 are transferred to theferromagnetic core portion 12 and a rotor shaft 14 through the permanentmagnetic 10. Such vibration is directly transferred up to a load sidethrough the rotor shaft 14, thereby amplifying mechanical vibrationnoise or causing resonance noise during the motor driving and increasingstress in a bearing while aggravating bearing noise, thus reducing theexpected life span of a motor.

In order to reduce vibration noise of the rotor of the conventional BLDCmotor, a sound-absorbing resin portion 13 such as rubber or siliconresin is inserted between the ferromagnetic core portion 12 and therotor shaft 14, thereby blocking noise and vibration transferred throughthe permanent magnetic 10 and the ferromagnetic core portion 12, asillustrated in FIG. 1B.

In this case, however, the use of the ferromagnetic core portion 12having a specific area is inevitable in order to minimize resistancebetween the armature 5 and the magnetic circuit 102 of the C-typepermanent magnet 10, as illustrated in FIG. 2.

Moreover, the use of the magnetic core portion 12 cannot greatly reducea weight of the rotor and the magnetic core portion 12 still acts as amedium through which cogging torque ripple, noise, or vibrationgenerated in the rotor is transferred. As a result, the use of thesound-absorbing resin portion 13 around the rotor shaft 14 for blockingvibration has a limitation in blocking noise and vibration.

Furthermore, for the conventional permanent magnet rotor, in order tocombine the C-type permanent magnet 10 with the ferromagnetic coreportion 12, a high-strength adhesive has to be used and the weightbalance of the rotor may be broken during adhesion between at least twopieces divided from the C-type permanence magnet 10.

The conventional BLDC motor has to use an electric steel sheet core soas to maintain the maximum magnetic flux density of the permanent magnetrotor and to minimize a loss of a rotating electric field. As a result,cogging torque vibration due to interaction with an armature core andelectromagnetic vibration noise of the rotating magnetic field areunavoidably transferred to a load side through the motor rotary shaft.

SUMMARY

Accordingly, an aspect of the embodiments discussed herein has been madein view of the above-mentioned problems occurring in the prior art, andit is an object of the present invention to provide a rotor of a BLDCmotor, in which a permanent magnet of the rotor is formed integrally ina ring shape as one piece and has a magnetic circuit therein, therebyremoving a need for a ferromagnetic for a separate magnetic circuitthrough which the magnetic flux of the permanent magnet can pass.

It is another aspect of the embodiments discussed herein to provide arotor of a BLDC motor, which can be made of a non-magnetic material or aplastic material, thereby blocking motor noise and vibration transferredthrough the rotor, reducing unnecessary weight and improving motor'spower-to-weight ratio and operating efficiency.

It is yet another aspect of the embodiments discussed herein to providea rotor of a BLDC motor, which can prevent a permanent magnet of therotor from being damaged by the thermal expansion of a sound-absorbingmaterial that is formed inside the cylindrical permanent magnet in orderto block noise.

To accomplish the above aspects, according to the embodiments discussedherein, there is provided a rotor of a brushless direct current (BLDC)motor, including: a cylindrical polar anisotropic permanent magnet forallowing a magnetized magnetic path to run therethrough; a high-strengthcore portion mounted on in the inner side of the polar anisotropicpermanent magnet; and a sound-absorbing resin portion mounted on theinner side of the high-strength core portion.

According to an aspect of the embodiments discussed herein, thethickness of the high-strength core portion is 40-100% of that of thepolar anisotropic permanent magnet.

Another aspect of the embodiments discussed herein, the high-strengthcore portion is formed of any one of non-magnetic metal, aluminum havinga low thermal expansion coefficient, alloy, or high-strength engineeringplastic.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the embodimentsdiscussed herein will be apparent from the following detaileddescription of the preferred embodiment of the invention in conjunctionwith the accompanying drawings, in which:

FIGS. IA and 1B illustrate the structure of a rotor of a conventionalBLDC motor;

FIG. 2 illustrates a magnetic circuit of the rotor and an armature ofthe conventional BLCD motor;

FIG. 3 illustrates the structure of a rotor of a BLDC motor according tothe embodiments discussed herein;

FIG. 4 illustrates a magnetic circuit of the rotor and an armature ofthe BLCD motor according to an aspect of the embodiments discussedherein;

FIG. 5 is a cross-sectional view showing the rotor of the BLDC motoraccording to an aspect of the embodiments discussed herein;

FIG. 6 is a perspective view showing the rotor of the BLDC motoraccording to an aspect of the embodiments discussed herein; and

FIGS. 7A through 7C are views showing comparison between a conventionaltechnique and an aspect of the embodiments discussed herein in order toexplain the effects of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings, wherein likereference numerals refer to the like elements throughout. Theembodiments are described below by referring to the figures.

FIG. 3 illustrates the structure of a rotor of a BLDC motor. Asillustrated in FIG. 3, the rotor includes a cylindrical permanent magnet1 and a cylindrical high-strength core portion 2 made of aluminum havinga very low thermal expansion coefficient, alloy, or high-strengthengineering plastic, which is adhered to the inner circumferentialportion of the permanent magnet 1.

It is preferable that in an embodiment the thickness of thehigh-strength core portion 2 can be 40-100% of that of the permanentmagnet 1.

In the rotor of an embodiment, the cylindrical high-strength coreportion 2 is inserted and adhered to an inner circumferential portion ofthe polar anisotropic permanent magnet 1, a sound-absorbing resinportion 3 made of rubber or sound-absorbing resin such as silicon resinis inserted and adhered to the inner circumferential portion of thehigh-strength core portion 2 to a thickness that can be two times thatof the cylindrical high-strength core portion 2, and a rotor shaft 4 isinserted into the center of the sound-absorbing resin portion 3.

For the high-strength core portion 2, a high-strength material havingsuperior heat-resisting property and a low thermal expansion coefficientis used, so as to prevent the cylindrical permanent magnet 1 from beingdamaged by the thermal expansion of the high-strength core portion 2 orthe thermal expansion of the sound-absorbing resin portion 3.

The permanent magnet 1 used for the rotor of an embodiment is acylindrical polar permanent magnet formed as one piece. The permanentmagnet 1 used in the present invention may be a polar anisotropicpermanent magnet, through which a magnetized magnetic path runs.

FIG. 4 illustrates a magnetic circuit 101 of the rotor 4 and an armature5 of the BLCD motor of an embodiment. The rotor 4 of an embodimentincludes the magnetic circuit 101 in which a flux flow 11 is formedwithin the cylindrical permanent magnet 1 as illustrated in FIG. 4.

FIG. 5 is a cross-sectional view showing the rotor of the BLDC motor ofan embodiment, and FIG. 6 is a perspective view showing the rotor of theBLDC motor of an embodiment.

As illustrated in FIGS. 5 and 6, the rotor of an embodiment is completedby assembling the cylindrical polar anisotropic permanent magnet 1, thecylindrical high-strength core portion 2 in the inner circumferentialportion of the permanent magnet 1, the sound-absorbing resin portion 3in the inner circumferential portion of the high-strength core portion2, and the rotor shaft 4 in the center of the sound-absorbing resinportion 3.

FIGS. 7A through 7C are views showing comparison between a conventionaltechnique and an embodiment in order to explain the effects of theembodiment. The amount of vibration transferred to the rotor shaft 14through a conventional permanent magnet rotor as indicated by 60 of FIG.7A or 61 of FIG. 7B is very large.

On the other hand, the rotor according to an embodiment uses thecylindrical polar anisotropic permanent magnet 1 formed as one piece,and a non-magnetic metal or high-strength plastic layer is primarilyformed and a sound-absorbing resin or sound-absorbing material layer issecondarily formed in the inner circumferential portion of the rotor,thereby greatly reducing the weight of the BLDC motor.

In other words, by reducing vibration and noise of a rotating magneticfield, which are transferred to the rotor shaft 4 through the rotor asindicated by 62 of FIG. 7C, by a large amount, mechanical noise andvibration in the motor and the load side can be reduced, contributing tothe extension of the life span of a bearing, the motor, and the loadside.

The rotor according to an embodiment has the magnetic field 101 in whichthe flux flow 11 is formed inside the cylindrical permanent magnet 1,without a need to form the path of the magnetic circuit 101 in thepermanent magnet 1 using a separate ferromagnetic as illustrated in FIG.3.

Consequently, the high-strength core portion 2 made of a non-magneticmaterial or plastic that is light and has superior vibration/noiseblocking property and the sound-absorbing resin portion 3 made ofsound-absorbing plastic resin or other sound-absorbing materials can beused sufficiently in an inner circumferential space of the polaranisotropic permanent magnet 1, and noise and vibration generated in theair gap 105 between the armature 5 and the permanent magnet 1 can beprevented from being transferred to the rotor shaft 14.

As set forth in the foregoing, the rotor according to an embodiment usesthe cylindrical polar anisotropic permanent magnet, and a non-magneticmetal or high-strength plastic layer is primarily formed and asound-absorbing resin or sound-absorbing material layer is secondarilyformed in the inner circumferential portion of the rotor, therebygreatly reducing the weight of the BLDC motor.

Moreover, by reducing vibration and noise of the rotating magnetic fieldtransferred to the rotary shaft through the rotor by a large amount,mechanical noise and vibration in the motor and the load side can begreatly reduced and the expected life span of the bearing, the motor,and other load sides can be extended.

While the present invention has been described with reference to theparticular illustrative embodiment, it is not to be restricted by theembodiment but only by the appended claims. It is to be appreciated thatthose skilled in the art can change or modify the embodiment withoutdeparting from the scope and spirit of the present invention.

1. A rotor of a BLDC (brushless direct current) motor, comprising: apolar anisotropic permanent magnet for allowing a magnetized magneticpath to run therethrough; a high-strength core portion mounted on theinner side of the polar anisotropic permanent magnet; and asound-absorbing resin portion mounted on the inner side of thehigh-strength core portion.
 2. The rotor of the BLDC motor according toclaim 1, wherein the thickness of the high-strength core portion is40-100% of that of the polar anisotropic permanent magnet.
 3. The rotorof the BLDC motor according to claim 1, wherein the high-strength coreportion is formed of any one of non-magnetic metal, aluminum having alow thermal expansion coefficient, alloy, or high-strength engineeringplastic.
 4. The rotor of the BLDC motor according to claim 1, whereinthe sound-absorbing resin is made of a rubber or a silicon resin.
 5. Therotor of the BLDC motor according to claim 1, wherein the polaranisotropic permanent magnetic is formed in a single body.
 6. The rotorof the BLDC motor according to claim 1, wherein the polar anisotropicpermanent magnetic is cylindrical shape.
 7. A rotor of a BLDC (brushlessdirect current) motor, comprising: a cylindrical permanent magnet forallowing a magnetized magnetic path to run therethrough; a high-strengthcore portion mounted on the inner side of the cylindrical permanentmagnet; and a sound-absorbing resin portion mounted on the inner side ofthe high-strength core portion.
 8. The rotator of a BLDC motor, whereinthe cylindrical permanent-magnetic is a polar anisotropicpermanent-magnetic.
 9. The rotator of a BLDC motor, wherein thehigh-strength core portion is formed of any one of non-magnetic metal,aluminum having a low thermal expansion coefficient, alloy, orhigh-strength engineering plastic
 10. The rotator of a BLDC motor,wherein the sound-absorbing resin portion is made of any one of a rubberand a silicon resin.
 11. A brushless direct current (BLDC) motor, themotor comprises the rotor of claim
 1. 12. A brushless direct current(BLDC) motor, the motor comprises the rotor of claim
 7. 13. A rotor of abrushless direct current motor, comprising: a magnet with rotor fluxflow completely inside the magnet; and a vibration blocking core.